Heretofore, high current density, long life scandate cathodes have generally been prepared by impregnating a porous tungsten billet with an impregnant such as Ba.sub.3 Al.sub.2 0.sub.6 followed by a layer of Sc.sub.2 (W0.sub.4).sub.3 deposited on the top of the impregnated billet. This has been done by mixing 1 mole of Sc.sub.2 0.sub.3 with 3 moles of W0.sub.3 to yield Sc.sub.2 (W0.sub.4).sub.3.
The foregoing method is not altogether satisfactory in that the generation of free barium for emission is limited to the amount of impregnant in the porous tungsten billet. This gives the cathode a limited life.